A typical microprocessor operated system control is responsive to a plurality of data inputs and provides at least one control output. For example, a typical system control for an air conditioning device such as a chiller or air handler would be responsive to such inputs as zone air temperature, supply air temperature, return air temperature, air velocity and so forth. In response to these inputs, the microprocessor of the system control will provide a control output to cause, for example, operation of the chiller or a change in air velocity supplied by the air handler. The microprocessor provides this control signal based upon instructions contained in a program or programs maintained in the controller and monitors the data input for compliance with the parameters called for in the program. In order to insure that the system controller is itself operating in conformity with the parameters set in the system control program, it is necessary to periodically monitor and diagnose the performance of the system controller.
Diagnostics of a system controller such as the foregoing typically is accomplished by providing subroutines in the main program of the system controller to provide data transmission through a data connector provided on the system controller. An interpreter or monitor device such as a computer or printer is connected to the data connector by a cable, and the data representing the current status of the system control is sent through cable to the monitor device. This method of transmitting the diagnostic data to the interpreting device requires the provision of a separate data output connector such as an industry standard RS-232, and in certain installations a controlling switch is also provided to permit an operator to activate the transmission of diagnostic data from the system controller. Furthermore, the cable connection to the data connector can alter the electrical characteristics of the system control circuitry, which may cause periodic or intermittent malfunctions to go undetected by the diagnostics device, or may even cause a malfunction false indication.
Alternatively, a monitor device may be attached by a permanent hard-wired connection to a system controller, permitting a diagnostic analysis of the system cpntroller data at any time. This method has the advantage of providing ongoing diagnostics of the system control and overcoming the object of providing a separate input output port or activation switch, as well as preventing alteration of the circuit characteristics of the system control. However, this method requires the use of a dedicated interpreting device, which is unnecessary and therefore unduly expensive in many applications, as it is often unnecessary to perform a diagnostic analysis of the system controller's performance barring an indication of improper operation. Therefore, the hard-wired connection is most suitable for application to installations having a relatively large number of system controllers and are therefore not as sensitive to the initial system cost and where ongoing monitoring of the system controller is desirable.
Since such system controllers are typically mass produced to meet requirements which vary widely from application to application, it is desirable to provide a means for diagnosing the operation of a system controller which is suitable for use in a broad range of applications. It is preferable to provide a system controller which is suitable for use in those systems which are cost. sensitive or do not require data interpretation and also for use in systems. Typically, an indicator is provided which permits a visual observation that the system controller is operating within the general limits specified by its program. The indicator is commonly a light source such as an LED (light emitting diode) having a specified pattern or cycle to indicate generally acceptable operation. For instance, the indicator may be a light source cyclically flashing one second ON and one second OFF, or two seconds ON and one second OFF, to indicate proper operation.
It is also possible include a read.out display and a controlling keypad or similar means of directing the diagnostics and data displayed to provide more specific information regarding the operation of the system controller. While this means provides an interface for a human operator at the site of the system controller, it involves unnecessary and undesirable additional expense and potential for unreliability due to the greatly increased number of components involved in the read.out display and keypad. Furthermore, in order to achieve complete diagnostic analysis of the system controller operation, it is still frequently necessary to provide the data connector for connection with a separate monitor device to eliminate the possibility of faulty internal self-diagnosis by the system controller's microprocessor.
Therefore, it is an object of the present invention to provide a method of diagnosing the operation of a system controller which is both simple and reliable.
It is a further object of subject invention to provide a method of diagnosis the operation of a system controller as will be suitable for mass production.
It is still a further object of the present invention to provide such a method for diagnosing the operation of a system controller as will be conducive to implementation in a wide range of applications.
It is yet a still further object of the present invention to provide such an apparatus which is suitable for cost sensitive installations while providing complete data transmission capabilities.
It is another object of the present invention to provide an apparatus for diagnosing the operation of a system controller without affecting the characteristics of the electrical circuitry of the system controller.
These and other objects of the invention will be apparent from the attached drawings and the Description of the Preferred Embodiment that follows hereinbelow.